Method for determining stress level of blade fatigue strength trafficability inspection

Abstract

The invention discloses a method for determining the stress level of blade fatigue strength trafficability inspection. The method comprises the following steps: setting a fatigue test cycle cardinal number; setting a fatigue life cycle number according to the fatigue test cycle cardinal number, and performing a fatigue test according to the fatigue life cycle number to obtain a fatigue strength limit; obtaining a fatigue logarithm data set according to the fatigue strength limit, and determining a fatigue curve equation according to the fatigue logarithm data set; calculating a fatigue strength logarithmic standard deviation according to the fatigue logarithmic data set and the fatigue curve equation; and calculating and determining the trafficability inspection stress level according to the fatigue strength logarithm standard deviation and the fatigue curve equation. According to the method, a fatigue curve equation is fitted according to blade fatigue strength data in combination with linear regression analysis and probability statistics theories, and the blade trafficability inspection stress level is determined.

Description

Technical Field

[0001] The invention belongs to the technical field of aerospace engine blades, and in particular relates to a method for determining a stress level of a blade fatigue strength passability inspection. Background Art

[0002] High-cycle fatigue failure is the most common failure form of aircraft engine blades. Very high requirements are placed on their high-cycle fatigue life and fatigue strength at the beginning of blade development and design. When developing aircraft engine blades, it is necessary to evaluate their fatigue strength limit under infinite fatigue life conditions. Since fatigue strength is very sensitive to the surface quality and process stability of the blades, fatigue strength passability inspection is a necessary inspection method for batch delivery and acceptance of blades. Its purpose is to eliminate minor changes in blade surface quality or process to verify whether the blades can reach the corresponding fatigue strength limit under infinite fatigue life conditions determined during development, and ensure that the blades have sufficient high-cycle fatigue life and fatigue strength.

[0003] At present, when performing fatigue strength inspection on aircraft engine blades, there is no specific method to determine the two important test parameters involved in the inspection: high-cycle fatigue cycle base and stress level. The usual practice is to directly select the fatigue strength limit σ determined according to infinite fatigue life during development. -1 , as the test stress level σ for passability check T , the stress level σ is not determined based on the determined passability inspection test cycle base T The current practice may cause the passability inspection test cycle base to be mismatched with the stress level, making the passability inspection test not equivalent to the fatigue strength limit test under infinite fatigue life conditions, resulting in inadequate blade assessment or stricter assessment.

[0004] For example, the Chinese patent with publication number CN117571289A discloses a blade vibration fatigue test device and test method. It includes: a vibration table is used to provide exciting force to the blade, and the blade is installed on the vibration table through a clamp; an acceleration sensor is used to collect the vibration acceleration signal output by the vibration table; a magnetic induction coil is set in the heating area of ​​the blade to heat the blade; a non-contact temperature sensor is used to measure the temperature of the blade; a strain gauge is attached to the maximum stress point of the blade to monitor the stress level of the blade; a displacement sensor is used to monitor the tip amplitude of the blade; a vibration controller is electrically connected to the vibration table, the acceleration sensor and the displacement sensor, and the vibration controller obtains the current resonance frequency according to the signal transmission relationship collected by the acceleration sensor and the displacement sensor, and analyzes and calculates the real-time resonance frequency by real-time tracking of the phase change of the resonance frequency. When the resonance frequency of the blade drops to a preset value, the vibration table stops vibrating. However, the patent does not make an accurate calculation and determination of the stress level of the blade fatigue test, which may result in the blade being under-assessed or under-assessed. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a method for determining the stress level of a blade fatigue strength passability inspection.

[0006] The present invention is achieved through the following technical solutions.

[0007] The present invention provides a method for determining a blade fatigue strength passability inspection stress level, comprising the following steps:

[0008] Set the fatigue test cycle base;

[0009] Set the number of fatigue life cycles according to the fatigue test cycle base, perform fatigue tests according to the number of fatigue life cycles, and obtain the fatigue strength limit;

[0010] Acquire a fatigue logarithmic data set according to the fatigue strength limit, and determine a fatigue curve equation according to the fatigue logarithmic data set, wherein the fatigue logarithmic data set includes a fatigue life logarithm and a fatigue strength logarithm;

[0011] Calculate the logarithmic standard deviation of fatigue strength based on the fatigue logarithmic data set and the fatigue curve equation;

[0012] The passability inspection stress level is determined by calculation based on the logarithmic standard deviation of fatigue strength and the fatigue curve equation.

[0013] Preferably, the fatigue life cycle number includes a first fatigue life cycle number and a second fatigue life cycle number, the first fatigue life cycle number is greater than the fatigue test cycle base number, and the second fatigue life cycle number is less than the fatigue test cycle base number;

[0014] The fatigue test according to the fatigue life cycle number adopts a step-by-step load increase method.

[0015] Preferably, obtaining the fatigue logarithmic data set according to the fatigue strength limit comprises the following steps:

[0016] Setting stress level conditions according to fatigue strength limit;

[0017] Perform fatigue tests according to stress level conditions to obtain fatigue data groups;

[0018] A fatigue logarithm data set is calculated from the fatigue data set.

[0019] Preferably, determining the fatigue curve equation according to the fatigue logarithmic data set comprises the following steps:

[0020] Calculate linear correlation coefficients based on fatigue logarithmic data sets;

[0021] Linear fitting is performed according to the linear correlation coefficient to obtain the fatigue curve equation.

[0022] Preferably, the linear fitting is performed using a least squares method.

[0023] Preferably, the expression of the linear correlation coefficient is as follows:

[0024]

[0025] Wherein, R is the linear correlation coefficient, Y is the logarithm of fatigue life in the fatigue logarithm data set, and X is the logarithm of fatigue strength in the fatigue logarithm data set.

[0026] Preferably, the step of calculating the fatigue strength logarithmic standard deviation according to the fatigue logarithmic data set and the fatigue curve equation comprises the following steps:

[0027] Calculate the standard deviation of the fatigue life logarithm according to the fatigue life logarithm in the fatigue life logarithm data group;

[0028] The logarithmic standard deviation of fatigue strength is calculated based on the logarithmic standard deviation of fatigue life and the fatigue curve equation.

[0029] Preferably, the expression for calculating the standard deviation of the fatigue life logarithm according to the fatigue life logarithm in the fatigue logarithm data set is as follows:

[0030]

[0031] Among them, S lgN is the logarithmic standard deviation of fatigue life, Y i is the logarithm of fatigue life in the fatigue logarithm data set, Y pi is the logarithm of fatigue life in the fatigue curve equation;

[0032] The expression for calculating the logarithmic standard deviation of fatigue strength based on the logarithmic standard deviation of fatigue life and the fatigue curve equation is as follows:

[0033]

[0034] Among them, S lgσ is the logarithmic standard deviation of fatigue strength, S lgN is the logarithmic standard deviation of fatigue life, and a is the linear coefficient in the fatigue curve equation.

[0035] Preferably, the calculation and determination of the passability inspection stress level according to the fatigue strength logarithmic standard deviation and the fatigue curve equation comprises the following steps:

[0036] Obtain failure probability of blade fatigue strength inspection;

[0037] The passability inspection stress level is determined by calculation based on the blade fatigue strength inspection failure probability, fatigue strength logarithmic standard deviation and fatigue curve equation.

[0038] Preferably, the expression for calculating and determining the passability inspection stress level according to the blade fatigue strength inspection failure probability, the fatigue strength logarithmic standard deviation and the fatigue curve equation is as follows:

[0039] lgσ T =lgσ NT -u p ×S lgσ

[0040] Among them, σ T For the passability check stress level, σ NT is the fatigue strength in the fatigue curve equation, u p is the standard normal deviator, p is the failure probability of blade fatigue strength inspection, S lgσ is the logarithmic standard deviation of fatigue strength.

[0041] The beneficial effects of the present invention are:

[0042] The present invention fits the fatigue curve equation based on the blade fatigue strength data, combined with linear regression analysis and probability statistics theory, and determines the blade passability inspection stress level. The calculation and determination of the blade fatigue strength passability inspection stress level is realized, which can make the passability inspection test equivalent to the fatigue strength limit test under infinite fatigue life conditions, making up for the direct selection of the fatigue strength limit σ in the prior art. -1 As a pass-through inspection test, the stress level can more truly reflect the surface quality and process stability of the blade, solve the problem of inadequate or stricter assessment of the blade, and make the fatigue strength test of the blade more real and reliable. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1It is a flow chart of the method provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0044] The technical solution of the present invention is further described below, but the scope of protection claimed is not limited to the description.

[0045] like Figure 1 As shown, a method for determining the stress level of a blade fatigue strength passability inspection comprises the following steps:

[0046] S1: Set the fatigue test cycle base;

[0047] Fatigue test cycle base N T There is no restriction on the selection, but it should be considered comprehensively based on factors such as blade material, infinite fatigue life, fatigue strength limit, and economy.

[0048] In this embodiment, considering the equivalent accuracy of the fatigue test of the blade passability inspection and the economy of the test, combined with the previous fatigue test experience, the fatigue test cycle base N is set T =2×10 6 .

[0049] S2: Set the number of fatigue life cycles according to the fatigue test cycle base, perform fatigue test according to the number of fatigue life cycles, and obtain the fatigue strength limit;

[0050] The fatigue life cycle number includes a first fatigue life cycle number and a second fatigue life cycle number, the first fatigue life cycle number is greater than the fatigue test cycle base number, and the second fatigue life cycle number is less than the fatigue test cycle base number;

[0051] To improve fatigue resistance, check the stress level σ T The estimation accuracy of the first fatigue life cycle number N 1 , the second fatigue life cycle number N 2 The selection principle should be to make σ T Try to be in the middle of the fatigue curve as much as possible and make the fatigue curve not too long.

[0052] In this embodiment, the cycle test base number N T =2×10 6 , the first fatigue life cycle number N 1 =10 7 , the second fatigue life cycle number N 2 =2×10 5 .

[0053] The fatigue test according to the fatigue life cycle number adopts a step-by-step load increase method.

[0054] Fatigue tests were carried out according to the number of fatigue life cycles. The fatigue tests on 4 blades were carried out using the step-by-step load increase method. The first fatigue life cycle number N 1 =10 7 With 2 blades, the second fatigue life cycle number N 2 =2×10 5 Fatigue tests were performed on 2 blades.

[0055] The step-by-step load increase method is used to determine the fatigue strength corresponding to different fatigue life cycle numbers of blades. It is a simple fatigue strength determination method that saves blades and time resources.

[0056] The initial level of fatigue test stress is selected, for N 1 =10 7 : For N 2 =2×10 5 : in Take the test results of the plate specimen, and the stress gradient Δσ is 40MPa.

[0057] The experimental results are shown in the following table:

[0058]

[0059] Among them, σ p is the stress level when the blade is damaged, N p is the stress level σ p The number of cycles before the upper blade fails. Fatigue strength is calculated according to the formula σ = σ p -Δσ / 2 calculation.

[0060] Get the fatigue strength limit σ N1 =740MPa,σ N2 =500MPa, fatigue strength limit σ N1 , σ N2 Determine the data point (σ N1 , N 1 )(σ N2 , N 2 ) as the upper and lower limits of the fatigue curve equation.

[0061] S3: acquiring a fatigue logarithmic data set according to the fatigue strength limit, and determining a fatigue curve equation according to the fatigue logarithmic data set, wherein the fatigue logarithmic data set includes a fatigue life logarithm and a fatigue strength logarithm;

[0062] The method of obtaining a fatigue logarithmic data set according to the fatigue strength limit comprises the following steps:

[0063] Setting stress level conditions according to fatigue strength limit;

[0064] In this embodiment, three stress level conditions are set, namely, σ N1 =740MPa,σ N2 =500MPa,

[0065] Perform fatigue tests according to stress level conditions to obtain fatigue data groups;

[0066] The fatigue data set is fatigue life N and fatigue strength σ.

[0067] A fatigue logarithm data set is calculated from the fatigue data set.

[0068] The fatigue logarithmic data set includes the logarithm of fatigue life lgN and the logarithm of fatigue strength lgσ.

[0069] In this embodiment, fatigue tests are performed on 6 blades under each stress level condition, and the fatigue life N of each test blade under each stress level condition is obtained. The test results are shown in the following table:

[0070]

[0071]

[0072] In the table, Y is the logarithm of fatigue life Y=lgN, and X is the logarithm of fatigue strength X=lgσ, that is, the fatigue logarithmic data set.

[0073] Determining the fatigue curve equation according to the fatigue logarithmic data set comprises the following steps:

[0074] Calculate linear correlation coefficients based on fatigue logarithmic data sets;

[0075] The expression of the linear correlation coefficient is as follows:

[0076]

[0077] Wherein, R is the linear correlation coefficient, Y is the logarithm of fatigue life in the fatigue logarithm data set, and X is the logarithm of fatigue strength in the fatigue logarithm data set.

[0078] In this embodiment, X=lgσ, Y=lgN, and the calculated linear correlation coefficient R=-0.93, which shows that X and Y are strongly linearly correlated.

[0079] Linear fitting is performed according to the linear correlation coefficient to obtain the fatigue curve equation.

[0080] In this embodiment, Y=aX+b is used as the fatigue curve equation.

[0081] The linear fitting is performed by using the least square method.

[0082] In this embodiment, the fitting results are Thus, the fatigue curve equation is obtained: Y=-10.37X+34.96.

[0083] S4: Calculate the logarithmic standard deviation of fatigue strength based on the fatigue logarithmic data set and the fatigue curve equation;

[0084] The calculation of the fatigue strength logarithmic standard deviation according to the fatigue logarithmic data set and the fatigue curve equation comprises the following steps:

[0085] Calculate the standard deviation of the fatigue life logarithm according to the fatigue life logarithm in the fatigue life logarithm data group;

[0086] The expression for calculating the standard deviation of the fatigue life logarithm according to the fatigue life logarithm in the fatigue logarithm data set is as follows:

[0087]

[0088] Among them, S lgN is the logarithmic standard deviation of fatigue life, Y i is the logarithm of fatigue life in the fatigue logarithm data set, Y pi is the logarithm of fatigue life in the fatigue curve equation;

[0089] The logarithmic standard deviation of fatigue strength is calculated based on the logarithmic standard deviation of fatigue life and the fatigue curve equation.

[0090] The expression for calculating the logarithmic standard deviation of fatigue strength based on the logarithmic standard deviation of fatigue life and the fatigue curve equation is as follows:

[0091]

[0092] Among them, S lgσ is the logarithmic standard deviation of fatigue strength, S lgN is the logarithmic standard deviation of fatigue life, and a is the linear coefficient in the fatigue curve equation.

[0093] In this embodiment, the fatigue strength logarithmic standard deviation S is calculated. lgσ =0.112, fatigue life logarithmic standard deviation S lgN =0.011.

[0094] S5: Determine the passability inspection stress level based on the logarithmic standard deviation of fatigue strength and the fatigue curve equation.

[0095] The method of calculating and determining the passability inspection stress level according to the fatigue strength logarithmic standard deviation and the fatigue curve equation comprises the following steps:

[0096] Obtain failure probability of blade fatigue strength inspection;

[0097] The failure probability of blade fatigue strength inspection is determined according to demand.

[0098] In this embodiment, the failure probability of blade fatigue strength inspection is set to p = 0.005, and the standard normal distribution table is consulted to obtain the standard normal deviation u p =2.576;

[0099] The passability inspection stress level is determined by calculation based on the blade fatigue strength inspection failure probability, fatigue strength logarithmic standard deviation and fatigue curve equation.

[0100] The expression for determining the passability inspection stress level according to the blade fatigue strength inspection failure probability, fatigue strength logarithmic standard deviation and fatigue curve equation is as follows:

[0101] lgσ T =lgσ NT -u p ×S lgσ

[0102] Among them, σ T For the passability check stress level, σ NT is the fatigue strength in the fatigue curve equation, u p is the standard normal deviator, p is the failure probability of blade fatigue strength inspection, S lgσ is the logarithmic standard deviation of fatigue strength.

[0103] In this embodiment, the above parameters are substituted into the calculation to determine σ T =543.6MPa.

[0104] The present invention fits the fatigue curve equation based on the blade fatigue strength data, combined with linear regression analysis and probability statistics theory, and determines the blade passability inspection stress level. The calculation and determination of the blade fatigue strength passability inspection stress level is realized, which can make the passability inspection test equivalent to the fatigue strength limit test under infinite fatigue life conditions, making up for the direct selection of the fatigue strength limit σ in the prior art. -1 As a pass-through inspection test, the stress level can more truly reflect the surface quality and process stability of the blade, solve the problem of inadequate or stricter assessment of the blade, and make the fatigue strength test of the blade more real and reliable.

Claims

1. A method for determining the stress level of a blade fatigue strength passability inspection, characterized in that: The following steps are involved: Set the fatigue test cycle base; Set the number of fatigue life cycles according to the fatigue test cycle base, perform fatigue tests according to the number of fatigue life cycles, and obtain the fatigue strength limit; Acquire a fatigue logarithmic data set according to the fatigue strength limit, and determine a fatigue curve equation according to the fatigue logarithmic data set, wherein the fatigue logarithmic data set includes a fatigue life logarithm and a fatigue strength logarithm; Calculate the logarithmic standard deviation of fatigue strength based on the fatigue logarithmic data set and the fatigue curve equation; The passability inspection stress level is determined by calculation based on the logarithmic standard deviation of fatigue strength and the fatigue curve equation.

2. The determination method according to claim 1, characterized in that: The fatigue life cycle number includes a first fatigue life cycle number and a second fatigue life cycle number, the first fatigue life cycle number is greater than the fatigue test cycle base number, and the second fatigue life cycle number is less than the fatigue test cycle base number; The fatigue test according to the fatigue life cycle number adopts a step-by-step load increase method.

3. The determination method according to claim 1, characterized in that: The method of obtaining a fatigue logarithmic data set according to the fatigue strength limit comprises the following steps: Setting stress level conditions according to fatigue strength limit; Perform fatigue tests according to stress level conditions to obtain fatigue data groups; A fatigue logarithm data set is calculated from the fatigue data set.

4. The determination method according to claim 1, characterized in that: Determining the fatigue curve equation according to the fatigue logarithmic data set comprises the following steps: Calculate linear correlation coefficients based on fatigue logarithmic data sets; Linear fitting is performed according to the linear correlation coefficient to obtain the fatigue curve equation.

5. The determination method according to claim 4, characterized in that: The linear fitting is performed by using the least square method.

6. The determination method according to claim 4, characterized in that: The expression of the linear correlation coefficient is as follows: Wherein, R is the linear correlation coefficient, Y is the logarithm of fatigue life in the fatigue logarithm data set, and X is the logarithm of fatigue strength in the fatigue logarithm data set.

7. The determination method according to claim 1, characterized in that: The calculation of the fatigue strength logarithmic standard deviation according to the fatigue logarithmic data set and the fatigue curve equation comprises the following steps: Calculate the standard deviation of the fatigue life logarithm according to the fatigue life logarithm in the fatigue life logarithm data group; The logarithmic standard deviation of fatigue strength is calculated based on the logarithmic standard deviation of fatigue life and the fatigue curve equation.

8. The determination method according to claim 7, characterized in that: The expression for calculating the standard deviation of the fatigue life logarithm according to the fatigue life logarithm in the fatigue logarithm data set is as follows: Among them, S lgN is the logarithmic standard deviation of fatigue life, Y i is the logarithm of fatigue life in the fatigue logarithm data set, Y pi is the logarithm of fatigue life in the fatigue curve equation; The expression for calculating the logarithmic standard deviation of fatigue strength based on the logarithmic standard deviation of fatigue life and the fatigue curve equation is as follows: Among them, S lgσ is the logarithmic standard deviation of fatigue strength, S lgN is the logarithmic standard deviation of fatigue life, and a is the linear coefficient in the fatigue curve equation.

9. The determination method according to claim 1, characterized in that: The method of calculating and determining the passability inspection stress level according to the fatigue strength logarithmic standard deviation and the fatigue curve equation comprises the following steps: Obtain failure probability of blade fatigue strength inspection; The passability inspection stress level is determined by calculation based on the blade fatigue strength inspection failure probability, fatigue strength logarithmic standard deviation and fatigue curve equation.

10. The determination method according to claim 9, characterized in that: The expression for determining the passability inspection stress level according to the blade fatigue strength inspection failure probability, fatigue strength logarithmic standard deviation and fatigue curve equation is as follows: lgσ T =lgσ NT -u p ×S lgσ Among them, σ T For the passability check stress level, σ NT is the fatigue strength in the fatigue curve equation, u p is the standard normal deviator, p is the failure probability of blade fatigue strength inspection, S lgσ is the logarithmic standard deviation of fatigue strength.

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